Due to the ease with which mouse cells can be established as continuous cell lines in vitro, it is possible to use mouse mutants that are presumed homologs of mutations in humans to determine the chromosomal localization of the human gene. In so doing, permanent mouse mutant cell lines and their hybrids with normal human cells are produced which can be useful for further studies concerning sub-chromosomal localization and the nature of the gene product, if this is not known. The beige mouse mutant (bgJ/bgJ) is considered a homolog of the Chediak-Higashi syndrome in humans. Both are inherited as autosomal recessive traits and involve the presence of dysmorphic intracellular organelles, including lysosomes and melanosomes, platelet storage pool deficiency and diminished immunological responsiveness. Beige mouse cells established in culture will be made HAT medium-sensitive and crossed with normal human cells to provide a panel of hybrid lines segregating for corrected (loss of dysmorphic granules) and uncorrected phenotypes. Hybrid lines will also be made by crossing the established beige mouse cells with normal human fibroblasts carrying the neoR gene and selecting for hybrids in G418 medium. Hybrids from both of these crosses will be assayed for human chromosome contents using isozyme markers, where it is anticipated that corrected lines will share a common human chromosome carrying the gene encoding for the correcting factor. Crosses of HAT medium-sensitive beige cells with Chediak- Higashi human cells will be used to determine the presumed homology between these two genes in these two species. As a first result, it will be possible to determine the chromosomal localization of the Chediak-Higashi gene in humans. These studies will also provide a direct test of the presumed homology of the beige mouse mutant with this human genetic disorder. They will also shed light on lysosomal pathophysiology and the genetic elements responsible for normal structure and function of these intracellular organelles.